Just like user plugins, the included Cells, Topologies, and Actions should be included in a system (i.e., installed where SEEDS is installed) plugins folder which is automatically appended/prepended to the plugin_dirs.
Make sure to explicitly state somewhere how the ordering of paths in the plugin_dirs matters. Will the first listed path always be the one chosen as with $PATH?
Just like user plugins, the included Cells, Topologies, and Actions should be included in a system (i.e., installed where SEEDS is installed) plugins folder which is automatically appended/prepended to the plugin_dirs.